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Volume 3, Issue 2
ISSN: 2470-9905
Crystallography 2017
October 16-17, 2017
2
nd
International Conference on
October 16-17, 2017 | Chicago, USA
Applied Crystallography
Hydrogen diffusion in nickel single- and poly-crystals: The effects of self-stress
H
ydrogen diffusion and trapping has an important role in solute-dependent hydrogen embrittlement in metals and metallic
alloys. In spite of extensive studies, the complexity of hydrogen diffusion in solids remains a phenomenon that needs to be
clarified. The effects of the grain boundaries (GBs), and several defects (dislocations, vacancies …) and their interactions with
hydrogen on the mechanisms of metal damages remain a controversy. Actually, several works suggest that the grain boundaries
represent preferential paths for hydrogen diffusion, and this kind of hydrogen diffusion along GBs is higher than the interstitial
diffusion. However, grains and GBs contain different defects, particularly, dislocations and vacancies. These defects are able to
trap hydrogen affecting the diffusion mechanisms. Although a number of theories have been proposed to describe the role of
GBs for hydrogen diffusion and segregation, none of them is able to give an exact answer. In present work we report our recent
works, which support the investigation of diffusion in pure nickel single crystals and poly-crystals using both an experimental
approach and a thermodynamic development. We have studied at the first time some nickel single crystals. We evaluate the
hydrogen diffusion and trapping mechanisms using the electrochemical permeation (EP) coupled to the thermal desorption
spectroscopy (TDS). Later, we propose to screen several bi-crystals of pure nickel with different grain boundaries. For each
ones, the hydrogen diffusion and segregation are studied using EP and TDS analyses. In addition, Molecular Dynamics (MD)
simulations have become a useful method to comprehend the becoming of hydrogen in these types of GBs. The results allow
us to associate the short-circuit diffusion and trapping phenomena to the grain boundaries and defect characters (excess
volume, defects density and distribution …). In each situation, we highlight the importance of the self-stress on the processes
of diffusion and segregation.
Biography
Professor Xavier Feaugas has published over three hundred papers, and several collective books in the field of physics, mechanics and metallurgy. His research
interests lie in the area of physical bases of solid plasticity and crack initiation with a focus on interactions between plasticity and surface reactivity to understand
the inception of hydrogen embrittlement and stress corrosion cracking. The main research topics are: physical bases of solid plasticity and crack initiation (disloca-
tion pattern, slip activity, slip, irreversibility, local approach of fracture …) - Interaction between plasticity and surface reactivity (dissolution, hydrogen adsorption,
passivity…) - Multi-physics modeling (ratcheting, cyclic over-hardening, hexagonal slip plasticity, thermo-kinetic modeling, polymer and composite degradation,
diffusion …) - Hydrogen Embrittlement/Stress Corrosion Cracking - Crystallographic defects (dislocation, vacancy, grain-boundaries, …), length scales, internal
stresses – physical and metallurgy thermodynamic. More recent trend of its works is focus on the different aspects of the interactions between the hydrogen solute
and the crystallographic defects formalized in thermodynamic framework.
xfeaugas@univ-lr.frXavier Feaugas
University of La Rochelle, France
Xavier Feaugas, Struct Chem Crystallogr Commun, 3:2
DOI: 10.21767/2470-9905-C1-001